PROTEIN-KINASE-C ISOFORM EXPRESSION DURING THE DIFFERENTIATION OF 3T3-L1 PREADIPOCYTES - LOSS OF PROTEIN-KINASE C-ALPHA ISOFORM CORRELATES WITH LOSS OF PHORBOL 12-MYRISTATE 13-ACETATE ACTIVATION OF NUCLEAR FACTOR KAPPA-B AND ACQUISITION OF THE ADIPOCYTE PHENOTYPE

The regulated expression of protein kinase C (PKC) isoforms was examin ed during the differentiation program of 3T3-L1 preadipocytes. In a pa rallel analysis, differentiation was blocked by treatment of the cells with tumor necrosis factor-alpha (TNF) to determine differentiation-s pecific changes in isoform expression from growth or treatment-induced effects. This analysis revealed that the expression of the convention al PKC-alpha isoform was reduced by 85% as cells attained the adipocyt e phenotype. PKC-beta expression was measurable only during the early stages of the differentiation process and was not detectable in fully differentiated cells. An upregulation of PKC-theta, a novel PKC isofor m, occurred during the latter stage of differentiation. Expression of PKC-zeta atypical PKC isoform suggested to participate in TNF signal t ransduction, occurred throughout the time course with similar levels o f expression in both preadipocytes and adipocytes, Nuclear run-on anal ysis demonstrated an approximate to 85% reduction in the transcription of the PKC-alpha gene during differentiation. the reduced expression of this isoform corresponded with the decreased ability to activate nu clear factor kappa B (NF-kappa B) in response to phorbol 12-myristate 13-acetate (PMA) treatment in the adipocytes. These data suggest that PMA responsiveness in 3T3-L1 adipocytes is markedly diminished. (C) 19 96 Wiley-Liss, Inc.